gistfile1.cpp

#include <boost/tuple/tuple.hpp>
#include <boost/iterator/iterator_facade.hpp>

struct triple_iterator: public boost::iterator_facade
                            <triple_iterator, boost::tuple<int, int, int> const,
                                boost::random_access_traversal_tag>
{
    int m;
    value_type value;

    triple_iterator(): m(1), value{3, 4, 5} {
    }

    bool equal (triple_iterator const& o) const {
        return m == o.m;
    }

    difference_type distance_to (triple_iterator const& o) const {
        return o.m - m;
    }

    void increment() { ++m; calc(); }
    void decrement() { --m; calc(); }
    void advance (difference_type x) { m += x; calc(); }
    reference dereference() const { return value; }

    void calc() {
        auto const n = m + 1;
        auto const nn = n*n;
        auto const mm = m*m;
        auto const nm = n*m;
        value = value_type { nn - mm, 2 * nm, nn + mm };
    }
};

#include <algorithm>
#include <iterator>
#include <iostream>
#include <boost/tuple/tuple_io.hpp>
namespace tuples = boost::tuples;

int main() {
    std::copy_n (triple_iterator(), 10,  std::ostream_iterator
                    <triple_iterator::value_type>(std::cout, "\n"));
}